The present invention relates to a method of producing a cathode ray tube, and particularly to a method of forming, on the inner surface of a panel, a metal back film, that is, a reflection film for improving the intensity of luminescence by a phosphor and a heat absorbing film for reducing the degree of mislanding of an electron beam due to thermal expansion of a mask used for color selection, and a method of forming films suitable for forming a reflection film and a heat absorbing film on the inner surface of a panel.
In the step of producing a panel of a color cathode ray tube, a phosphor film is formed on the inner surface of a panel and then a reflection film made from aluminum is formed on the phosphor film.
The phosphor film is formed by forming phosphors of red, green, and blue on a black matrix film already formed on the inner surface of the panel at specific positions corresponding to a specific pattern, and forming an intermediate film for smoothening the surfaces of the phosphors thereon.
The reflection film is formed by vapor-depositing aluminum on the inner surface of the panel on which the phosphor film has been formed.
In this way, as shown in FIG. 1, a phosphor film 2 and a reflection film 3 are formed on the inner surface of the panel 1.
In a color cathode ray tube, generally, three electron beams emitted from an electron gun are subjected to color selection by a so-called mask such as an aperture grill or a shadow mask.
The three electron beams, which have passed through the mask, collide with phosphors of the corresponding colors.
When irradiated with the electron beams, the mask generates heat, with a result that the temperature of the mask is increased.
The temperature of the mask is further increased due to the fact that the radiation heat of the mask is reflected from the reflection film formed on the phosphor film.
As a result, the thermal expansion of the mask becomes significant, resulting in a deviation in landing position of each electron beam when the electron beam reaches the phosphor.
The deviation in landing position of each electron beam is called xe2x80x9cmislandingxe2x80x9d of the electron beam.
Such a phenomenon causes an inconvenience such as color shift on an image displayed on a screen of the cathode ray tube.
To reduce the degree of mislanding of electron beams, there have been known methods of forming a heat absorbing film on a reflection film already formed on the inner surface of a panel.
The heat absorbing film functions to absorb the radiation heat generated by a mask.
The use of the heat absorbing film is thus effective to suppress the thermal expansion of the mask.
According to the related art methods, the reflection film is first formed by vapor-depositing aluminum on the inner surface of the panel, and then the heat absorbing film is formed thereon.
For example, according to one of the related art methods, a heat absorbing film is formed on the inner surface of a panel, on which a reflection film has been formed, by coating the inner surface of the panel with a suspension of graphite by spraying.
According to another related art method, aluminum is vapor-deposited to form a reflection film, and subsequently aluminum is again vapor-deposited at a vacuum pressure higher than a vacuum pressure set at the time of forming the reflection film, to form a heat absorbing film made from aluminum oxide on the reflection film.
According to a further related art method, a heat absorbing film is formed by vapor-depositing a blackened material other than aluminum, for example, manganese or tin.
Each of the above-described related art methods, however, requires independent two film formation steps for forming a reflection film and a heat absorbing film on the inner surface of a panel.
As an inconvenient result, the process of producing a panel of a cathode ray tube is complicated.
An object of the present invention is to provide a method of forming a reflection film and a heat absorbing film on the inner surface of a panel of a cathode ray tube without complicating a process of producing the cathode ray tube.
To achieve the above object, according to the present invention, there is provided a method of producing a cathode ray tube, which is adapted to form a reflection film and a heat absorbing film on the inner surface of a panel by using a vacuum vapor-deposition process, including the steps of: supplying a first material for forming the reflection film and a second material for forming the heat absorbing film to a heating source; and heating and vaporizing the first and second materials by the heating source, thereby depositing the first and second materials on the inner surface of the panel; wherein the second material has a boiling point under a vacuum pressure at the time of vapor-deposition, which is higher than that of the first material.
With this configuration, when the first and second materials supplied to the heating source are heated by the heat source, the first material lower in boiling pressure under a vacuum pressure at the time of vapor-deposition is first vaporized to be deposited on the inner surface of the panel, and then the second material is vaporized to be deposited on the inner surface of the panel.
As a result, the reflection film and the heat absorbing film are continuously formed in one vapor-deposition step.
This is effective to simplify the process of producing a cathode ray tube and hence to reduce the production cost thereof.